The present invention relates to a method for assessing color performance in a printing device.
In a printing apparatus, for example an inkjet printer, there is the need to assess the accuracy of the colors printed by the device. For instance, a user may have the perception that the printed colors are not consistent from time to time, or that some colors do not correspond to their intended subject, for example skin tones or corporate colors; it may also happen that grey tones are not neutral but are biased towards a particular color. Thus, the printing device may have errors in its color performance.
However, the cause for color errors is not always a failure or malfunctioning of the printing device. Colors may be modified by the printer settings, for example if some ink emulations are selected; and even applications external to the printing device, such as image processing software, may also influence the colors which are printed in the printing device.
Therefore, when dealing with color issues it is necessary to assess if any trouble with the printed colors is caused by the printing device itself.
In case it is determined that indeed the color performance of the printing device is not correct, it is also desirable to ascertain which of the color channels is causing the trouble, and to quantify the error in order to solve the problem.
Some traditional methods for assessing color performance involve printing a test or demo sheet and compare it to an external color reference; however, especially in case of remote troubleshooting, an external reference is not always available, and has a number of drawbacks. Sophisticated tools such as spectrophotometers are costly and are not suitable for normal technical support work; Pantone color tables and similar references may fade with time and are not always at hand.
On the other hand, in many cases it would be useful to verify if there is a malfunctioning of the printing device remotely, without the need for on-site technical support visits; this is difficult to achieve while relying on an external reference.
U.S. Pat. No. 6,215,562 and U.S. Pat. No. 5,604,567 disclose methods for visual calibration of a color printer based on iterative processes.
U.S. Pat. No. 5,604,567 describes a process in which a test pattern with a plurality of color patches is printed and the most grey patch of the test pattern is visually selected for performing color correction; after a first correction, the test pattern is printed again and the process is repeated as many times as necessary. This method avoid the use of sophisticated tools; however, the selection of the most grey patch may not be easy and introduces a degree of uncertainty in the method; furthermore, it requires several printing and correcting steps.
Embodiments of the present invention provide a method for assessing color performance in a printing device in a fast and reliable way. Further embodiments of the invention ameliorate other drawbacks mentioned in the prior art.
According to an aspect of the present invention, a method for assessing color performance in a printing device, which is provided with color printing means for printing at least three primary color inks, comprises the steps of:
(a) providing a printing file for printing at least one color scale, said scale comprising:
a plurality of colored regions defined by substantially equal amounts of a first primary color ink and of a second primary color ink and a variable amount of a third primary color ink, said amount of third primary color ink increasing progressively from each region to the adjacent region in one direction of the scale, and
a transition region defined by substantially equal amounts of the three primary color inks;
(b) printing said printing file with said printing device to obtain a printed color scale; and
(c) visually analysing the printed color scale to assess the performance of said color printing means for printing said third primary color ink, on the basis of the position of the transition region along the color scale.
The method allows to assess easily the performance of the printing device ; this is due to the fact that with a scale defined according to the invention, the visual identification of the transition region is possible without the need for an external reference. Furthermore, in case of malfunctioning of the color printing means, the method allows to quantify the error and thus perform the required correction.
The existence of an error and its quantification are decided in a single operation, i. e. printing and visually analysing the color scale once.
The printing and analysis of the color scale can be performed on-site by technical support staff or simply by the user, without the need for a visit of the support staff.
In embodiments of the invent ion, said printing file contains an independent color scale for each of said primary color inks, and said step (c) comprises visually analysing the printed color scales to assess the performance of said color printing means for printing each of the three primary color inks, on the basis of the position of the transition region along each color scale.
By this method, the performances of the three primary color inks can be verified and quantified in the same operation, simply printing and analysing the printing file.
According to some embodiments, said scale has a number of regions between 5 and 20.
Optionally, a numerical scale is printed along said color scale, such as to make it easier to check if the transition region is in the foreseen position and to quantify any error.
Said printing file may further provide a dark region defined by large predetermined amounts of each of the three primary color inks, said dark region being arranged such that it is printed prior to said color scale.
Printing these dark regions enhances the color accuracy of the scale, because it helps to avoid small errors due to heat-up of the pen.
According to embodiments of the invention, said printing file further provides a grey background defined by a predetermined amount of black ink, against which said color scale is printed.
This neutral grey background reduces the contrast with the color scales; it has been found that this makes the visual evaluation of the transition region easier than when a white background is used, especially if the file is printed on glossy printing media.
In embodiments of the invention, said primary color inks comprise Cyan, Magenta and Yellow.
The printing file may include a TIF image file with said color scale.
According to some embodiments, the printing file further comprises predetermined settings for the printing device.
The predetermined settings may include disabling any ink emulation or color rendering that may alter the colors defined in the printing file.
These features help to avoid errors when printing the color scales, such as wrong settings inputted by the user that may modify the printed colors.
According to some embodiments, said printing file is included in the machine code of the printing device, and preferably it is such that it cannot b e modified by a user, such that any alteration of the colors set in the printing file is avoided.
The printing device may be an inkjet printer, and said color printing means may be inkjet printheads.
According to another aspect, the present invention relates to a method for assessing color performance in a printing device provided with color printing means for printing at least three primary color inks, wherein said method comprises the steps of:
(a) providing a printing file for printing at least three independent color scales, one associated to each primary color ink, each scale comprising:
a plurality of colored regions defined by a variable amount of one primary color ink associated to the scale, the amount of said one primary color ink increasing progressively from each region to the adjacent region in one direction of the scale, and equal amounts of two other primary color inks, and
a transition region defined by substantially equal amounts of the three primary color inks;
(b) printing said printing file with said printing device to obtain the printed color scales; and
(c) visually analysing each printed color scale to assess the performance of said color printing means for printing each primary color ink, on the basis of the position of the transition region along each color scale.
According to a further aspect the invention relates to a method for color calibrating a printing device provided with color printing means for printing at least three primary color inks, wherein said method comprises the steps of:
(a) providing a printing file for printing at least one color scale, said scale comprising:
a plurality of colored regions defined by substantially equal amounts of a first primary color ink and of a second primary color ink and a variable amount of a third primary color ink, said amount of third primary color ink increasing progressively from each region to the adjacent region in one direction of the scale, and
a transition region defined by substantially equal amounts of the three primary color inks;
(b) printing said printing file with said printing device to obtain a printed color scale; and
(c) visually analysing the printed color scale to assess the performance of said color printing means for printing said third primary color ink, on the basis of the position of the transition region along the color scale; and
(d) color calibrating said color printing means for printing said third primary color ink in the printing device, according to the performance assessment of step (c).
In embodiments of this method, said printing file contains an independent color scale for each of said primary color inks, said step (c) comprises visually analysing the printed color scales to assess the performance of said color printing means for printing each of the three primary color inks, on the basis of the position of the transition region along each color scale, and said step (d) comprises color calibrating said color printing means for printing each primary color ink in the printing device, according to the performance assessment of step (c).
Yet another aspect of the present invention relates to a printing file containing at least one color scale, said scale comprising:
a plurality of colored regions defined by substantially equal amounts of a first primary color ink and of a second primary color ink, and a variable amount of a third primary color ink, said amount of third primary color ink increasing progressively from each region to the adjacent region in one direction of the scale, and
a transition region defined by substantially equal amounts of the three primary color inks.
The printing file may be used in methods according to the invention, for assessing the color performance of a printing device in a fast and simple way.
Said printing file may further comprise a grey background defined by a predetermined amount of black ink, against which said color scale is printed.
In embodiments of the invention, the printing file further comprises predetermined settings for a printing device.
According to another aspect, the present invention relates to an inkjet printer provided with printheads for at least three primary color inks and comprising a printing file as described above.